The results obtained by our research work from 1993 to 1995 are summarized as follows.1.Determination of the unitary distance of actin-myosin sliding per ATP molecule : We activated single glycerinated muscle fibers by laser flash photolysis of caged ATP,and measured the relation between the amount of photoreleased ATP and the distance of myofilament sliding. It was found that the minimum uniform fiber shortening (about 10 nm/half sarcomere) was produced when the number of ATP molecules was the same as the number of myosin molecules within the fiber. We also examined the distance of sliding between myosin-coated glass microneedles and actin filament arrays caused by iontophoretic application of ATP,and found that the minimum actin-myosin sliding distance was also about 10 nm.2.Measurement of the efficiency of chemo-mechanical energy conversion in muscle fibers : We activated single glycerinated muscle fibers, which contained ATP molecules equal to the myosin heads in number, by laser flash photlysis of caged Ca. The amount of ATP utilized was estimated by releasing the fiber to zero force level, and measuring the subsequent development of isometric force. The results showed that the amount of ATP utilized increased in proportion to the distance shortened, while the amount of work done by the fiber was bell-shaped, being zero in the isometric and free-loaded conditions. This indicates that the efficiency of chemo-mechanical energy conversion in the individual myosin heads differs greatly in a load-dependent manner.3.Force-velocity relation of actin-myosin sliding causing cytoplasmic streaming in plant cells : We determined the force-velocity relation of actin-myosin sliding in algal cells, and found that the very high free-loaded sliding velocity is associated with low efficiency of energy conversion.